El Nino and hurricanes produce repetitive flash flooding in coastal Alabama

Mobile AL is one of the wettest major cities in the United States, averaging 64 inches annually. However, the period from May 1997 to September 1998 was exceptionally wet with at least 5 extraordinary rainfall events occurring in Mobile County, 4 of which exceeded a 100 year return frequency. A total of 135.51" fell at the Mobile National Weather Service office (KMOB) during this 17 month period, an excess of 40.95". This period encompassed two hurricane landfalls in the area (Danny and Georges), and the effects of the massive 1997-98 El Nino.

Three of these events were associated with extratropical mesoscale convective systems. Each produced 100 year rainfall events at the Coastal Weather Research Center on the campus of the University of South Alabama (USA) in Mobile. Flash flooding resulted in 3 drowning deaths at an intersection over Twelve-mile Creek adjacent to the university. These events were associated with line echo wave patterns along slow moving squall lines which produced training of embedded convection. Torrential rainfall rates accompanied each event with 4.52" in one hour on 28 May 97, 5.54" in two hours on 7 Jan 98, and 6.54" in three hours on 7 Mar 98 at the USA campus.

The other two events accompanied tropical cyclone landfalls. Hurricane Danny (July 1997) produced a precipitation event of biblical proportions when 36.71 inches of rain fell over the southern end of Mobile County. Finally, Hurricane Georges produced over 15 inches of rainfall at KMOB during its slow trek across coastal Alabama. Bay Minette AL in neighboring Baldwin Co received nearly 30" of rainfall during Georges.